Re: [PATCH] kcsan: Add test suite

[Paul E. McKenney]

On Mon, Apr 27, 2020 at 05:23:23PM +0200, Marco Elver wrote:
> On Mon, 27 Apr 2020 at 16:35, Marco Elver <elver@xxxxxxxxxx> wrote:
> >
> > This adds KCSAN test focusing on behaviour of the integrated runtime.
> > Tests various race scenarios, and verifies the reports generated to
> > console. Makes use of KUnit for test organization, and the Torture
> > framework for test thread control.
> >
> > Signed-off-by: Marco Elver <elver@xxxxxxxxxx>
> > ---
> 
> +KUnit devs
> We had some discussions on how to best test sanitizer runtimes, and we
> believe that this test is what testing sanitizer runtimes should
> roughly look like. Note that, for KCSAN there are various additional
> complexities like multiple threads, and report generation isn't
> entirely deterministic (need to run some number of iterations to get
> reports, may get multiple reports, etc.).
> 
> The main thing, however, is that we want to verify the actual output
> (or absence of it) to console. This is what the KCSAN test does using
> the 'console' tracepoint. Could KUnit provide some generic
> infrastructure to check console output, like is done in the test here?
> Right now I couldn't say what the most useful generalization of this
> would be (without it just being a wrapper around the console
> tracepoint), because the way I've decided to capture and then match
> console output is quite test-specific. For now we can replicate this
> logic on a per-test basis, but it would be extremely useful if there
> was a generic interface that KUnit could provide in future.
> 
> Thoughts?

What I do in rcutorture is to run in a VM, dump the console output
to a file, then parse that output after the run completes.  For example,
the admittedly crude script here:

	tools/testing/selftests/rcutorture/bin/parse-console.sh

							Thanx, Paul

> Thanks,
> -- Marco
> 
> >  kernel/kcsan/Makefile     |    3 +
> >  kernel/kcsan/kcsan-test.c | 1067 +++++++++++++++++++++++++++++++++++++
> >  lib/Kconfig.kcsan         |   23 +-
> >  3 files changed, 1092 insertions(+), 1 deletion(-)
> >  create mode 100644 kernel/kcsan/kcsan-test.c
> >
> > diff --git a/kernel/kcsan/Makefile b/kernel/kcsan/Makefile
> > index d4999b38d1be..14533cf24bc3 100644
> > --- a/kernel/kcsan/Makefile
> > +++ b/kernel/kcsan/Makefile
> > @@ -12,3 +12,6 @@ CFLAGS_core.o := $(call cc-option,-fno-conserve-stack,) \
> >
> >  obj-y := core.o debugfs.o report.o
> >  obj-$(CONFIG_KCSAN_SELFTEST) += test.o
> > +
> > +CFLAGS_kcsan-test.o := $(CFLAGS_KCSAN) -g -fno-omit-frame-pointer
> > +obj-$(CONFIG_KCSAN_TEST) += kcsan-test.o
> > diff --git a/kernel/kcsan/kcsan-test.c b/kernel/kcsan/kcsan-test.c
> > new file mode 100644
> > index 000000000000..04326cd5a4b2
> > --- /dev/null
> > +++ b/kernel/kcsan/kcsan-test.c
> > @@ -0,0 +1,1067 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * KCSAN test with various race scenarious to test runtime behaviour. Since the
> > + * interface with which KCSAN's reports are obtained is via the console, this is
> > + * the output we should verify. For each test case checks the presence (or
> > + * absence) of generated reports. Relies on 'console' tracepoint to capture
> > + * reports as they appear in the kernel log.
> > + *
> > + * Makes use of KUnit for test organization, and the Torture framework for test
> > + * thread control.
> > + *
> > + * Copyright (C) 2020, Google LLC.
> > + * Author: Marco Elver <elver@xxxxxxxxxx>
> > + */
> > +
> > +#include <kunit/test.h>
> > +#include <linux/jiffies.h>
> > +#include <linux/kcsan-checks.h>
> > +#include <linux/kernel.h>
> > +#include <linux/sched.h>
> > +#include <linux/seqlock.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/string.h>
> > +#include <linux/timer.h>
> > +#include <linux/torture.h>
> > +#include <linux/tracepoint.h>
> > +#include <linux/types.h>
> > +#include <trace/events/printk.h>
> > +
> > +/* Points to current test-case memory access "kernels". */
> > +static void (*access_kernels[2])(void);
> > +
> > +static struct task_struct **threads; /* Lists of threads. */
> > +static unsigned long end_time;       /* End time of test. */
> > +
> > +/* Report as observed from console. */
> > +static struct {
> > +       spinlock_t lock;
> > +       int nlines;
> > +       char lines[3][512];
> > +} observed = {
> > +       .lock = __SPIN_LOCK_UNLOCKED(observed.lock),
> > +};
> > +
> > +/* Setup test checking loop. */
> > +static __no_kcsan_or_inline void
> > +begin_test_checks(void (*func1)(void), void (*func2)(void))
> > +{
> > +       kcsan_disable_current();
> > +
> > +       /*
> > +        * Require at least as long as KCSAN_REPORT_ONCE_IN_MS, to ensure at
> > +        * least one race is reported.
> > +        */
> > +       end_time = jiffies + msecs_to_jiffies(CONFIG_KCSAN_REPORT_ONCE_IN_MS + 300);
> > +
> > +       /* Signal start; release potential initialization of shared data. */
> > +       smp_store_release(&access_kernels[0], func1);
> > +       smp_store_release(&access_kernels[1], func2);
> > +}
> > +
> > +/* End test checking loop. */
> > +static __no_kcsan_or_inline bool
> > +end_test_checks(bool stop)
> > +{
> > +       if (!stop && time_before(jiffies, end_time)) {
> > +               /* Continue checking */
> > +               return false;
> > +       }
> > +
> > +       kcsan_enable_current();
> > +       return true;
> > +}
> > +
> > +/*
> > + * Probe for console output: checks if a race was reported, and obtains observed
> > + * lines of interest.
> > + */
> > +__no_kcsan
> > +static void probe_console(void *ignore, const char *buf, size_t len)
> > +{
> > +       unsigned long flags;
> > +       int nlines;
> > +
> > +       /*
> > +        * Note that KCSAN reports under a global lock, so we do not risk the
> > +        * possibility of having multiple reports interleaved. If that were the
> > +        * case, we'd expect tests to fail.
> > +        */
> > +
> > +       spin_lock_irqsave(&observed.lock, flags);
> > +       nlines = observed.nlines;
> > +
> > +       if (strnstr(buf, "BUG: KCSAN: ", len) && strnstr(buf, "test_", len)) {
> > +               /*
> > +                * KCSAN report and related to the test.
> > +                *
> > +                * The provided @buf is not NUL-terminated; copy no more than
> > +                * @len bytes and let strscpy() add the missing NUL-terminator.
> > +                */
> > +               strscpy(observed.lines[0], buf, min(len + 1, sizeof(observed.lines[0])));
> > +               nlines = 1;
> > +       } else if ((nlines == 1 || nlines == 2) && strnstr(buf, "bytes by", len)) {
> > +               strscpy(observed.lines[nlines++], buf, min(len + 1, sizeof(observed.lines[0])));
> > +
> > +               if (strnstr(buf, "race at unknown origin", len)) {
> > +                       if (WARN_ON(nlines != 2))
> > +                               goto out;
> > +
> > +                       /* No second line of interest. */
> > +                       strcpy(observed.lines[nlines++], "<none>");
> > +               }
> > +       }
> > +
> > +out:
> > +       WRITE_ONCE(observed.nlines, nlines); /* Publish new nlines. */
> > +       spin_unlock_irqrestore(&observed.lock, flags);
> > +}
> > +
> > +/* Check if a report related to the test exists. */
> > +__no_kcsan
> > +static bool report_available(void)
> > +{
> > +       return READ_ONCE(observed.nlines) == ARRAY_SIZE(observed.lines);
> > +}
> > +
> > +/* Report information we expect in a report. */
> > +struct expect_report {
> > +       /* Access information of both accesses. */
> > +       struct {
> > +               void *fn;    /* Function pointer to expected function of top frame. */
> > +               void *addr;  /* Address of access; unchecked if NULL. */
> > +               size_t size; /* Size of access; unchecked if @addr is NULL. */
> > +               int type;    /* Access type, see KCSAN_ACCESS definitions. */
> > +       } access[2];
> > +};
> > +
> > +/* Check observed report matches information in @r. */
> > +__no_kcsan
> > +static bool report_matches(const struct expect_report *r)
> > +{
> > +       const bool is_assert = (r->access[0].type | r->access[1].type) & KCSAN_ACCESS_ASSERT;
> > +       bool ret = false;
> > +       unsigned long flags;
> > +       typeof(observed.lines) expect;
> > +       const char *end;
> > +       char *cur;
> > +       int i;
> > +
> > +       /* Doubled-checked locking. */
> > +       if (!report_available())
> > +               return false;
> > +
> > +       /* Generate expected report contents. */
> > +
> > +       /* Title */
> > +       cur = expect[0];
> > +       end = &expect[0][sizeof(expect[0]) - 1];
> > +       cur += scnprintf(cur, end - cur, "BUG: KCSAN: %s in ",
> > +                        is_assert ? "assert: race" : "data-race");
> > +       if (r->access[1].fn) {
> > +               char tmp[2][64];
> > +               int cmp;
> > +
> > +               /* Expect lexographically sorted function names in title. */
> > +               scnprintf(tmp[0], sizeof(tmp[0]), "%pS", r->access[0].fn);
> > +               scnprintf(tmp[1], sizeof(tmp[1]), "%pS", r->access[1].fn);
> > +               cmp = strcmp(tmp[0], tmp[1]);
> > +               cur += scnprintf(cur, end - cur, "%ps / %ps",
> > +                                cmp < 0 ? r->access[0].fn : r->access[1].fn,
> > +                                cmp < 0 ? r->access[1].fn : r->access[0].fn);
> > +       } else {
> > +               scnprintf(cur, end - cur, "%pS", r->access[0].fn);
> > +               /* The exact offset won't match, remove it. */
> > +               cur = strchr(expect[0], '+');
> > +               if (cur)
> > +                       *cur = '\0';
> > +       }
> > +
> > +       /* Access 1 */
> > +       cur = expect[1];
> > +       end = &expect[1][sizeof(expect[1]) - 1];
> > +       if (!r->access[1].fn)
> > +               cur += scnprintf(cur, end - cur, "race at unknown origin, with ");
> > +
> > +       /* Access 1 & 2 */
> > +       for (i = 0; i < 2; ++i) {
> > +               const char *const access_type =
> > +                       (r->access[i].type & KCSAN_ACCESS_ASSERT) ?
> > +                               ((r->access[i].type & KCSAN_ACCESS_WRITE) ?
> > +                                        "assert no accesses" :
> > +                                        "assert no writes") :
> > +                               ((r->access[i].type & KCSAN_ACCESS_WRITE) ?
> > +                                        "write" :
> > +                                        "read");
> > +               const char *const access_type_aux =
> > +                       (r->access[i].type & KCSAN_ACCESS_ATOMIC) ?
> > +                               " (marked)" :
> > +                               ((r->access[i].type & KCSAN_ACCESS_SCOPED) ?
> > +                                        " (scoped)" :
> > +                                        "");
> > +
> > +               if (i == 1) {
> > +                       /* Access 2 */
> > +                       cur = expect[2];
> > +                       end = &expect[2][sizeof(expect[2]) - 1];
> > +
> > +                       if (!r->access[1].fn) {
> > +                               /* Dummy string if no second access is available. */
> > +                               strcpy(cur, "<none>");
> > +                               break;
> > +                       }
> > +               }
> > +
> > +               cur += scnprintf(cur, end - cur, "%s%s to ", access_type,
> > +                                access_type_aux);
> > +
> > +               if (r->access[i].addr) /* Address is optional. */
> > +                       cur += scnprintf(cur, end - cur, "0x%px of %zu bytes",
> > +                                        r->access[i].addr, r->access[i].size);
> > +       }
> > +
> > +       spin_lock_irqsave(&observed.lock, flags);
> > +       if (!report_available())
> > +               goto out; /* A new report is being captured. */
> > +
> > +       /* Finally match expected output to what we actually observed. */
> > +       ret = strstr(observed.lines[0], expect[0]) &&
> > +             /* Access info may appear in any order. */
> > +             ((strstr(observed.lines[1], expect[1]) &&
> > +               strstr(observed.lines[2], expect[2])) ||
> > +              (strstr(observed.lines[1], expect[2]) &&
> > +               strstr(observed.lines[2], expect[1])));
> > +out:
> > +       spin_unlock_irqrestore(&observed.lock, flags);
> > +       return ret;
> > +}
> > +
> > +/* ===== Test kernels ===== */
> > +
> > +static long test_sink;
> > +static long test_var;
> > +/* @test_array should be large enough to fall into multiple watchpoint slots. */
> > +static long test_array[3 * PAGE_SIZE / sizeof(long)];
> > +static struct {
> > +       long val[8];
> > +} test_struct;
> > +static DEFINE_SEQLOCK(test_seqlock);
> > +
> > +/*
> > + * Helper to avoid compiler optimizing out reads, and to generate source values
> > + * for writes.
> > + */
> > +__no_kcsan
> > +static noinline void sink_value(long v) { WRITE_ONCE(test_sink, v); }
> > +
> > +static noinline void test_kernel_read(void) { sink_value(test_var); }
> > +
> > +static noinline void test_kernel_write(void)
> > +{
> > +       test_var = READ_ONCE_NOCHECK(test_sink) + 1;
> > +}
> > +
> > +static noinline void test_kernel_write_nochange(void) { test_var = 42; }
> > +
> > +/* Suffixed by value-change exception filter. */
> > +static noinline void test_kernel_write_nochange_rcu(void) { test_var = 42; }
> > +
> > +static noinline void test_kernel_read_atomic(void)
> > +{
> > +       sink_value(READ_ONCE(test_var));
> > +}
> > +
> > +static noinline void test_kernel_write_atomic(void)
> > +{
> > +       WRITE_ONCE(test_var, READ_ONCE_NOCHECK(test_sink) + 1);
> > +}
> > +
> > +__no_kcsan
> > +static noinline void test_kernel_write_uninstrumented(void) { test_var++; }
> > +
> > +static noinline void test_kernel_data_race(void) { data_race(test_var++); }
> > +
> > +static noinline void test_kernel_assert_writer(void)
> > +{
> > +       ASSERT_EXCLUSIVE_WRITER(test_var);
> > +}
> > +
> > +static noinline void test_kernel_assert_access(void)
> > +{
> > +       ASSERT_EXCLUSIVE_ACCESS(test_var);
> > +}
> > +
> > +#define TEST_CHANGE_BITS 0xff00ff00
> > +
> > +static noinline void test_kernel_change_bits(void)
> > +{
> > +       if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS)) {
> > +               /*
> > +                * Avoid race of unknown origin for this test, just pretend they
> > +                * are atomic.
> > +                */
> > +               kcsan_nestable_atomic_begin();
> > +               test_var ^= TEST_CHANGE_BITS;
> > +               kcsan_nestable_atomic_end();
> > +       } else
> > +               WRITE_ONCE(test_var, READ_ONCE(test_var) ^ TEST_CHANGE_BITS);
> > +}
> > +
> > +static noinline void test_kernel_assert_bits_change(void)
> > +{
> > +       ASSERT_EXCLUSIVE_BITS(test_var, TEST_CHANGE_BITS);
> > +}
> > +
> > +static noinline void test_kernel_assert_bits_nochange(void)
> > +{
> > +       ASSERT_EXCLUSIVE_BITS(test_var, ~TEST_CHANGE_BITS);
> > +}
> > +
> > +/* To check that scoped assertions do trigger anywhere in scope. */
> > +static noinline void test_enter_scope(void)
> > +{
> > +       int x = 0;
> > +
> > +       /* Unrelated accesses to scoped assert. */
> > +       READ_ONCE(test_sink);
> > +       kcsan_check_read(&x, sizeof(x));
> > +}
> > +
> > +static noinline void test_kernel_assert_writer_scoped(void)
> > +{
> > +       ASSERT_EXCLUSIVE_WRITER_SCOPED(test_var);
> > +       test_enter_scope();
> > +}
> > +
> > +static noinline void test_kernel_assert_access_scoped(void)
> > +{
> > +       ASSERT_EXCLUSIVE_ACCESS_SCOPED(test_var);
> > +       test_enter_scope();
> > +}
> > +
> > +static noinline void test_kernel_rmw_array(void)
> > +{
> > +       int i;
> > +
> > +       for (i = 0; i < ARRAY_SIZE(test_array); ++i)
> > +               test_array[i]++;
> > +}
> > +
> > +static noinline void test_kernel_write_struct(void)
> > +{
> > +       kcsan_check_write(&test_struct, sizeof(test_struct));
> > +       kcsan_disable_current();
> > +       test_struct.val[3]++; /* induce value change */
> > +       kcsan_enable_current();
> > +}
> > +
> > +static noinline void test_kernel_write_struct_part(void)
> > +{
> > +       test_struct.val[3] = 42;
> > +}
> > +
> > +static noinline void test_kernel_read_struct_zero_size(void)
> > +{
> > +       kcsan_check_read(&test_struct.val[3], 0);
> > +}
> > +
> > +static noinline void test_kernel_seqlock_reader(void)
> > +{
> > +       unsigned int seq;
> > +
> > +       do {
> > +               seq = read_seqbegin(&test_seqlock);
> > +               sink_value(test_var);
> > +       } while (read_seqretry(&test_seqlock, seq));
> > +}
> > +
> > +static noinline void test_kernel_seqlock_writer(void)
> > +{
> > +       unsigned long flags;
> > +
> > +       write_seqlock_irqsave(&test_seqlock, flags);
> > +       test_var++;
> > +       write_sequnlock_irqrestore(&test_seqlock, flags);
> > +}
> > +
> > +/* ===== Test cases ===== */
> > +
> > +/* Simple test with normal data race. */
> > +__no_kcsan
> > +static void test_basic(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       static const struct expect_report never = {
> > +               .access = {
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_write, test_kernel_read);
> > +       do {
> > +               match_expect |= report_matches(&expect);
> > +               match_never = report_matches(&never);
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +/*
> > + * Stress KCSAN with lots of concurrent races on different addresses until
> > + * timeout.
> > + */
> > +__no_kcsan
> > +static void test_concurrent_races(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       /* NULL will match any address. */
> > +                       { test_kernel_rmw_array, NULL, 0, KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_rmw_array, NULL, 0, 0 },
> > +               },
> > +       };
> > +       static const struct expect_report never = {
> > +               .access = {
> > +                       { test_kernel_rmw_array, NULL, 0, 0 },
> > +                       { test_kernel_rmw_array, NULL, 0, 0 },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_rmw_array, test_kernel_rmw_array);
> > +       do {
> > +               match_expect |= report_matches(&expect);
> > +               match_never |= report_matches(&never);
> > +       } while (!end_test_checks(false));
> > +       KUNIT_EXPECT_TRUE(test, match_expect); /* Sanity check matches exist. */
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +/* Test the KCSAN_REPORT_VALUE_CHANGE_ONLY option. */
> > +__no_kcsan
> > +static void test_novalue_change(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_write_nochange, test_kernel_read);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       if (IS_ENABLED(CONFIG_KCSAN_REPORT_VALUE_CHANGE_ONLY))
> > +               KUNIT_EXPECT_FALSE(test, match_expect);
> > +       else
> > +               KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +/*
> > + * Test that the rules where the KCSAN_REPORT_VALUE_CHANGE_ONLY option should
> > + * never apply work.
> > + */
> > +__no_kcsan
> > +static void test_novalue_change_exception(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write_nochange_rcu, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_write_nochange_rcu, test_kernel_read);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +/* Test that data races of unknown origin are reported. */
> > +__no_kcsan
> > +static void test_unknown_origin(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +                       { NULL },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_write_uninstrumented, test_kernel_read);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       if (IS_ENABLED(CONFIG_KCSAN_REPORT_RACE_UNKNOWN_ORIGIN))
> > +               KUNIT_EXPECT_TRUE(test, match_expect);
> > +       else
> > +               KUNIT_EXPECT_FALSE(test, match_expect);
> > +}
> > +
> > +/* Test KCSAN_ASSUME_PLAIN_WRITES_ATOMIC if it is selected. */
> > +__no_kcsan
> > +static void test_write_write_assume_atomic(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_write, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_write, test_kernel_write);
> > +       do {
> > +               sink_value(READ_ONCE(test_var)); /* induce value-change */
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       if (IS_ENABLED(CONFIG_KCSAN_ASSUME_PLAIN_WRITES_ATOMIC))
> > +               KUNIT_EXPECT_FALSE(test, match_expect);
> > +       else
> > +               KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +/*
> > + * Test that data races with writes larger than word-size are always reported,
> > + * even if KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected.
> > + */
> > +__no_kcsan
> > +static void test_write_write_struct(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_write_struct, test_kernel_write_struct);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +/*
> > + * Test that data races where only one write is larger than word-size are always
> > + * reported, even if KCSAN_ASSUME_PLAIN_WRITES_ATOMIC is selected.
> > + */
> > +__no_kcsan
> > +static void test_write_write_struct_part(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_write_struct_part, &test_struct.val[3], sizeof(test_struct.val[3]), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_write_struct, test_kernel_write_struct_part);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +/* Test that races with atomic accesses never result in reports. */
> > +__no_kcsan
> > +static void test_read_atomic_write_atomic(struct kunit *test)
> > +{
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_read_atomic, test_kernel_write_atomic);
> > +       do {
> > +               match_never = report_available();
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +/* Test that a race with an atomic and plain access result in reports. */
> > +__no_kcsan
> > +static void test_read_plain_atomic_write(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +                       { test_kernel_write_atomic, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE | KCSAN_ACCESS_ATOMIC },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       if (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS))
> > +               return;
> > +
> > +       begin_test_checks(test_kernel_read, test_kernel_write_atomic);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +/* Zero-sized accesses should never cause data race reports. */
> > +__no_kcsan
> > +static void test_zero_size_access(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       const struct expect_report never = {
> > +               .access = {
> > +                       { test_kernel_write_struct, &test_struct, sizeof(test_struct), KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_read_struct_zero_size, &test_struct.val[3], 0, 0 },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_write_struct, test_kernel_read_struct_zero_size);
> > +       do {
> > +               match_expect |= report_matches(&expect);
> > +               match_never = report_matches(&never);
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_TRUE(test, match_expect); /* Sanity check. */
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +/* Test the data_race() macro. */
> > +__no_kcsan
> > +static void test_data_race(struct kunit *test)
> > +{
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_data_race, test_kernel_data_race);
> > +       do {
> > +               match_never = report_available();
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_writer(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> > +                       { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_assert_writer, test_kernel_write_nochange);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_access(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_assert_access, test_kernel_read);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_access_writer(struct kunit *test)
> > +{
> > +       const struct expect_report expect_access_writer = {
> > +               .access = {
> > +                       { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> > +               },
> > +       };
> > +       const struct expect_report expect_access_access = {
> > +               .access = {
> > +                       { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> > +                       { test_kernel_assert_access, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       const struct expect_report never = {
> > +               .access = {
> > +                       { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> > +                       { test_kernel_assert_writer, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> > +               },
> > +       };
> > +       bool match_expect_access_writer = false;
> > +       bool match_expect_access_access = false;
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_assert_access, test_kernel_assert_writer);
> > +       do {
> > +               match_expect_access_writer |= report_matches(&expect_access_writer);
> > +               match_expect_access_access |= report_matches(&expect_access_access);
> > +               match_never |= report_matches(&never);
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_TRUE(test, match_expect_access_writer);
> > +       KUNIT_EXPECT_TRUE(test, match_expect_access_access);
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_bits_change(struct kunit *test)
> > +{
> > +       const struct expect_report expect = {
> > +               .access = {
> > +                       { test_kernel_assert_bits_change, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT },
> > +                       { test_kernel_change_bits, &test_var, sizeof(test_var),
> > +                               KCSAN_ACCESS_WRITE | (IS_ENABLED(CONFIG_KCSAN_IGNORE_ATOMICS) ? 0 : KCSAN_ACCESS_ATOMIC) },
> > +               },
> > +       };
> > +       bool match_expect = false;
> > +
> > +       begin_test_checks(test_kernel_assert_bits_change, test_kernel_change_bits);
> > +       do {
> > +               match_expect = report_matches(&expect);
> > +       } while (!end_test_checks(match_expect));
> > +       KUNIT_EXPECT_TRUE(test, match_expect);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_bits_nochange(struct kunit *test)
> > +{
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_assert_bits_nochange, test_kernel_change_bits);
> > +       do {
> > +               match_never = report_available();
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_writer_scoped(struct kunit *test)
> > +{
> > +       const struct expect_report expect_start = {
> > +               .access = {
> > +                       { test_kernel_assert_writer_scoped, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_SCOPED },
> > +                       { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       const struct expect_report expect_anywhere = {
> > +               .access = {
> > +                       { test_enter_scope, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_SCOPED },
> > +                       { test_kernel_write_nochange, &test_var, sizeof(test_var), KCSAN_ACCESS_WRITE },
> > +               },
> > +       };
> > +       bool match_expect_start = false;
> > +       bool match_expect_anywhere = false;
> > +
> > +       begin_test_checks(test_kernel_assert_writer_scoped, test_kernel_write_nochange);
> > +       do {
> > +               match_expect_start |= report_matches(&expect_start);
> > +               match_expect_anywhere |= report_matches(&expect_anywhere);
> > +       } while (!end_test_checks(match_expect_start && match_expect_anywhere));
> > +       KUNIT_EXPECT_TRUE(test, match_expect_start);
> > +       KUNIT_EXPECT_TRUE(test, match_expect_anywhere);
> > +}
> > +
> > +__no_kcsan
> > +static void test_assert_exclusive_access_scoped(struct kunit *test)
> > +{
> > +       const struct expect_report expect_start1 = {
> > +               .access = {
> > +                       { test_kernel_assert_access_scoped, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_SCOPED },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       const struct expect_report expect_start2 = {
> > +               .access = { expect_start1.access[0], expect_start1.access[0] },
> > +       };
> > +       const struct expect_report expect_inscope = {
> > +               .access = {
> > +                       { test_enter_scope, &test_var, sizeof(test_var), KCSAN_ACCESS_ASSERT | KCSAN_ACCESS_WRITE | KCSAN_ACCESS_SCOPED },
> > +                       { test_kernel_read, &test_var, sizeof(test_var), 0 },
> > +               },
> > +       };
> > +       bool match_expect_start = false;
> > +       bool match_expect_inscope = false;
> > +
> > +       begin_test_checks(test_kernel_assert_access_scoped, test_kernel_read);
> > +       end_time += msecs_to_jiffies(1000); /* This test requires a bit more time. */
> > +       do {
> > +               match_expect_start |= report_matches(&expect_start1) || report_matches(&expect_start2);
> > +               match_expect_inscope |= report_matches(&expect_inscope);
> > +       } while (!end_test_checks(match_expect_start && match_expect_inscope));
> > +       KUNIT_EXPECT_TRUE(test, match_expect_start);
> > +       KUNIT_EXPECT_TRUE(test, match_expect_inscope);
> > +}
> > +
> > +/* Test that racing accesses in seqlock critical sections are not reported. */
> > +__no_kcsan
> > +static void test_seqlock_noreport(struct kunit *test)
> > +{
> > +       bool match_never = false;
> > +
> > +       begin_test_checks(test_kernel_seqlock_reader, test_kernel_seqlock_writer);
> > +       do {
> > +               match_never = report_available();
> > +       } while (!end_test_checks(match_never));
> > +       KUNIT_EXPECT_FALSE(test, match_never);
> > +}
> > +
> > +/*
> > + * Each test case is run with different numbers of threads. Until KUnit supports
> > + * passing arguments for each test case, we encode #threads in the test case
> > + * name (read by get_num_threads()). [The '-' was chosen as a stylistic
> > + * preference to separate test name and #threads.]
> > + *
> > + * The thread counts are chosen to cover potentially interesting boundaries and
> > + * corner cases (range 2-5), and then stress the system with larger counts.
> > + */
> > +#define KCSAN_KUNIT_CASE(test_name)                                            \
> > +       { .run_case = test_name, .name = #test_name "-02" },                   \
> > +       { .run_case = test_name, .name = #test_name "-03" },                   \
> > +       { .run_case = test_name, .name = #test_name "-04" },                   \
> > +       { .run_case = test_name, .name = #test_name "-05" },                   \
> > +       { .run_case = test_name, .name = #test_name "-08" },                   \
> > +       { .run_case = test_name, .name = #test_name "-16" }
> > +
> > +static struct kunit_case kcsan_test_cases[] = {
> > +       KCSAN_KUNIT_CASE(test_basic),
> > +       KCSAN_KUNIT_CASE(test_concurrent_races),
> > +       KCSAN_KUNIT_CASE(test_novalue_change),
> > +       KCSAN_KUNIT_CASE(test_novalue_change_exception),
> > +       KCSAN_KUNIT_CASE(test_unknown_origin),
> > +       KCSAN_KUNIT_CASE(test_write_write_assume_atomic),
> > +       KCSAN_KUNIT_CASE(test_write_write_struct),
> > +       KCSAN_KUNIT_CASE(test_write_write_struct_part),
> > +       KCSAN_KUNIT_CASE(test_read_atomic_write_atomic),
> > +       KCSAN_KUNIT_CASE(test_read_plain_atomic_write),
> > +       KCSAN_KUNIT_CASE(test_zero_size_access),
> > +       KCSAN_KUNIT_CASE(test_data_race),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_writer),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_access),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_access_writer),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_bits_change),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_bits_nochange),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_writer_scoped),
> > +       KCSAN_KUNIT_CASE(test_assert_exclusive_access_scoped),
> > +       KCSAN_KUNIT_CASE(test_seqlock_noreport),
> > +       {},
> > +};
> > +
> > +/* ===== End test cases ===== */
> > +
> > +/* Get number of threads encoded in test name. */
> > +static bool __no_kcsan
> > +get_num_threads(const char *test, int *nthreads)
> > +{
> > +       int len = strlen(test);
> > +
> > +       if (WARN_ON(len < 3))
> > +               return false;
> > +
> > +       *nthreads = test[len - 1] - '0';
> > +       *nthreads += (test[len - 2] - '0') * 10;
> > +
> > +       if (WARN_ON(*nthreads < 0))
> > +               return false;
> > +
> > +       return true;
> > +}
> > +
> > +/* Concurrent accesses from interrupts. */
> > +__no_kcsan
> > +static void access_thread_timer(struct timer_list *timer)
> > +{
> > +       static atomic_t cnt = ATOMIC_INIT(0);
> > +       unsigned int idx;
> > +       void (*func)(void);
> > +
> > +       idx = (unsigned int)atomic_inc_return(&cnt) % ARRAY_SIZE(access_kernels);
> > +       /* Acquire potential initialization. */
> > +       func = smp_load_acquire(&access_kernels[idx]);
> > +       if (func)
> > +               func();
> > +}
> > +
> > +/* The main loop for each thread. */
> > +__no_kcsan
> > +static int access_thread(void *arg)
> > +{
> > +       struct timer_list timer;
> > +       unsigned int cnt = 0;
> > +       unsigned int idx;
> > +       void (*func)(void);
> > +
> > +       timer_setup_on_stack(&timer, access_thread_timer, 0);
> > +       do {
> > +               if (!timer_pending(&timer))
> > +                       mod_timer(&timer, jiffies + 1);
> > +               else {
> > +                       /* Iterate through all kernels. */
> > +                       idx = cnt++ % ARRAY_SIZE(access_kernels);
> > +                       /* Acquire potential initialization. */
> > +                       func = smp_load_acquire(&access_kernels[idx]);
> > +                       if (func)
> > +                               func();
> > +               }
> > +       } while (!torture_must_stop());
> > +       del_timer_sync(&timer);
> > +       destroy_timer_on_stack(&timer);
> > +
> > +       torture_kthread_stopping("access_thread");
> > +       return 0;
> > +}
> > +
> > +__no_kcsan
> > +static int test_init(struct kunit *test)
> > +{
> > +       unsigned long flags;
> > +       int nthreads;
> > +       int i;
> > +
> > +       spin_lock_irqsave(&observed.lock, flags);
> > +       for (i = 0; i < ARRAY_SIZE(observed.lines); ++i)
> > +               observed.lines[i][0] = '\0';
> > +       observed.nlines = 0;
> > +       spin_unlock_irqrestore(&observed.lock, flags);
> > +
> > +       if (!torture_init_begin((char *)test->name, 1))
> > +               return -EBUSY;
> > +
> > +       if (!get_num_threads(test->name, &nthreads))
> > +               goto err;
> > +
> > +       if (WARN_ON(threads))
> > +               goto err;
> > +
> > +       for (i = 0; i < ARRAY_SIZE(access_kernels); ++i) {
> > +               if (WARN_ON(access_kernels[i]))
> > +                       goto err;
> > +       }
> > +
> > +       if (!IS_ENABLED(CONFIG_PREEMPT) && nthreads > num_online_cpus() - 2) {
> > +               nthreads = num_online_cpus() - 2;
> > +               pr_info("%s: limiting number of threads to %d\n", test->name,
> > +                       nthreads);
> > +       }
> > +
> > +       if (nthreads) {
> > +               threads = kcalloc(nthreads + 1, sizeof(struct task_struct *),
> > +                                 GFP_KERNEL);
> > +               if (WARN_ON(!threads))
> > +                       goto err;
> > +
> > +               threads[nthreads] = NULL;
> > +               for (i = 0; i < nthreads; ++i) {
> > +                       if (torture_create_kthread(access_thread, NULL,
> > +                                                  threads[i]))
> > +                               goto err;
> > +               }
> > +       }
> > +
> > +       torture_init_end();
> > +
> > +       return 0;
> > +
> > +err:
> > +       kfree(threads);
> > +       threads = NULL;
> > +       torture_init_end();
> > +       return -EINVAL;
> > +}
> > +
> > +__no_kcsan
> > +static void test_exit(struct kunit *test)
> > +{
> > +       struct task_struct **stop_thread;
> > +       int i;
> > +
> > +       if (torture_cleanup_begin())
> > +               return;
> > +
> > +       for (i = 0; i < ARRAY_SIZE(access_kernels); ++i)
> > +               WRITE_ONCE(access_kernels[i], NULL);
> > +
> > +       if (threads) {
> > +               for (stop_thread = threads; *stop_thread; stop_thread++)
> > +                       torture_stop_kthread(reader_thread, *stop_thread);
> > +
> > +               kfree(threads);
> > +               threads = NULL;
> > +       }
> > +
> > +       torture_cleanup_end();
> > +}
> > +
> > +static struct kunit_suite kcsan_test_suite = {
> > +       .name = "kcsan-test",
> > +       .test_cases = kcsan_test_cases,
> > +       .init = test_init,
> > +       .exit = test_exit,
> > +};
> > +static struct kunit_suite *kcsan_test_suites[] = { &kcsan_test_suite, NULL };
> > +
> > +__no_kcsan
> > +static void register_tracepoints(struct tracepoint *tp, void *ignore)
> > +{
> > +       check_trace_callback_type_console(probe_console);
> > +       if (!strcmp(tp->name, "console"))
> > +               WARN_ON(tracepoint_probe_register(tp, probe_console, NULL));
> > +}
> > +
> > +__no_kcsan
> > +static void unregister_tracepoints(struct tracepoint *tp, void *ignore)
> > +{
> > +       if (!strcmp(tp->name, "console"))
> > +               tracepoint_probe_unregister(tp, probe_console, NULL);
> > +}
> > +
> > +/*
> > + * We only want to do tracepoints setup and teardown once, therefore we have to
> > + * customize the init and exit functions and cannot rely on kunit_test_suite().
> > + */
> > +static int __init kcsan_test_init(void)
> > +{
> > +       /*
> > +        * Because we want to be able to build the test as a module, we need to
> > +        * iterate through all known tracepoints, since the static registration
> > +        * won't work here.
> > +        */
> > +       for_each_kernel_tracepoint(register_tracepoints, NULL);
> > +       return __kunit_test_suites_init(kcsan_test_suites);
> > +}
> > +
> > +static void kcsan_test_exit(void)
> > +{
> > +       __kunit_test_suites_exit(kcsan_test_suites);
> > +       for_each_kernel_tracepoint(unregister_tracepoints, NULL);
> > +       tracepoint_synchronize_unregister();
> > +}
> > +
> > +late_initcall(kcsan_test_init);
> > +module_exit(kcsan_test_exit);
> > +
> > +MODULE_LICENSE("GPL v2");
> > +MODULE_AUTHOR("Marco Elver <elver@xxxxxxxxxx>");
> > diff --git a/lib/Kconfig.kcsan b/lib/Kconfig.kcsan
> > index 689b6b81f272..ea28245c6c1d 100644
> > --- a/lib/Kconfig.kcsan
> > +++ b/lib/Kconfig.kcsan
> > @@ -41,7 +41,28 @@ config KCSAN_SELFTEST
> >         bool "Perform short selftests on boot"
> >         default y
> >         help
> > -         Run KCSAN selftests on boot. On test failure, causes the kernel to panic.
> > +         Run KCSAN selftests on boot. On test failure, causes the kernel to
> > +         panic. Recommended to be enabled, ensuring critical functionality
> > +         works as intended.
> > +
> > +config KCSAN_TEST
> > +       tristate "KCSAN test for integrated runtime behaviour"
> > +       depends on TRACEPOINTS && KUNIT
> > +       select TORTURE_TEST
> > +       help
> > +         KCSAN test focusing on behaviour of the integrated runtime. Tests
> > +         various race scenarios, and verifies the reports generated to
> > +         console. Makes use of KUnit for test organization, and the Torture
> > +         framework for test thread control.
> > +
> > +         Each test case may run at least up to KCSAN_REPORT_ONCE_IN_MS
> > +         milliseconds. Test run duration may be optimized by building the
> > +         kernel and KCSAN test with KCSAN_REPORT_ONCE_IN_MS set to a lower
> > +         than default value.
> > +
> > +         Say Y here if you want the test to be built into the kernel and run
> > +         during boot; say M if you want the test to build as a module; say N
> > +         if you are unsure.
> >
> >  config KCSAN_EARLY_ENABLE
> >         bool "Early enable during boot"
> > --
> > 2.26.2.303.gf8c07b1a785-goog
> >